Doug Brunk is with the San Diego bureau of Elsevier Global Medical News.
Extended-duration antiviral prophylaxis against pandemic and seasonal influenza appears to be effective in immunocompetent adults, including nursing home patients. Also, extended-duration oseltamivir is associated with increased nausea and vomiting, compared with zanamivir.
Those are findings from a systematic review of seven published randomized, double-blind, placebo-controlled trials of extended-duration (exceeding 4 weeks) neuraminidase inhibitor (NAI) prophylaxis. All trials reported outcomes of laboratory-confirmed influenza or adverse events.
“Until new antiviral agents are available, and while oseltamivir and zanamivir remain our main antiviral options against seasonal and pandemic influenza, we encourage research on the safety of extended-duration zanamivir and oseltamivir chemoprophylaxis in children and the development of zanamivir formulations that can be delivered safely and effectively to young children, patients with obstructive lung diseases, and elderly individuals,” the investigators wrote in the Annals of Internal Medicine and online.
The team was led by Nayer Khazeni, MD, of the division of pulmonary and critical care medicine at Stanford (Calif.) University.
“With these cautions, zanamivir can currently be used in immunocompetent adults without obstructive lung disease to decrease the risk for symptomatic influenza illness when there is a need for extended-duration chemoprophylaxis against seasonal influenza, and it can be stockpiled to distribute to these same individuals for chemoprophylaxis against pandemic influenza.”
The studies reviewed were published between 1999 and 2007. The seven trials studied included 7,021 patients. More than half of the patients (a median of 63%) were female, and six of the seven studies included those who were predominately white (a median of 87%). Most of the studies were conducted in outpatient settings, while one was conducted in a nursing home.
Dr. Khazeni and associates classified study participants as having positive or negative outcomes for symptomatic influenza virus infection, symptomatic influenza, or adverse events and then calculated the relative risk (RR) for each outcome of interest.
The researchers found that NAI prophylaxis decreased the frequency of symptomatic influenza (RR 0.26) but not asymptomatic influenza (RR 1.03).
NAI use was not associated with an increase in adverse events overall, but nausea and vomiting occurred more often in patients who took oseltamivir (RR 1.48). The absolute risk of nausea and vomiting with oseltamivir was from 2% to 15%. No difference in the prevention of influenza was seen between the two treatment groups.
The researchers acknowledged limitations of their review, including the fact that all trials were sponsored by the pharmaceutical industry and none included diverse racial groups, children, or immunocompromised patients.
“Roche is conducting a trial of extended-duration (12 weeks) oseltamivir chemoprophylaxis in immunocompromised individuals; we advocate that the findings of that trial be closely reviewed in the context of our results,” the researchers said. The researchers disclosed no conflict of interest.
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